Here's how to toggle notifications from the website you're currently on:
Browser: Firefox 44
Find the address bar at the top of the browser. To the left of it and to the right of the "back" button is a symbol (it may look like a globe or something else). Click the symbol. In the menu that opens there is a section called "Permissions" and under it the dropdown for selecting "Show Notifications". You may choose to Block, Allow, or Always Ask from there.